PROJECT SUMMARY: The overall goal of the studies in this project is to test the hypothesis that inflammatory endotypes control clinical presentations and comorbid airway diseases in chronic rhinosinusitis (CRS). CRS is one of the most common chronic diseases in adults in the US, affecting approximately 12.5% of Americans, and has a severe impact on patients' quality of life and healthcare costs. Although CRS is most commonly treated with antibiotics, steroids, and allergy medications, their efficacy is not universal. Due to poor responses to medical therapy, over 400,000 surgical procedures are performed annually in the US. There is therefore an urgent need for a new understanding of the pathogenic mechanisms that drive CRS phenotypes. CRS is clinically classified into CRS with nasal polyps (CRSwNP) and CRS without nasal polyps (CRSsNP). Both forms are characterized by intense inflammatory cell infiltration which drives symptoms of the disease, but CRSwNP is the more severe form of the two and is characterized by type 2 inflammation including eosinophilia. In contrast to CRSwNP, the mechanism of inflammation in CRSsNP is understudied and poorly understood, despite the fact that over 75% of CRS patients have this phenotype. Although initial studies from Europe suggested that CRSsNP is characterized by type 1 inflammation, we found that only a small subset of patients with CRSsNP did show type 1 inflammation. We therefore hypothesized that inflammation in CRSsNP is more heterogeneous than CRSwNP and this induces variable outcomes of medical treatment. In a preliminary study, we found the overall frequency of CRSsNP with type 1, 2 and 3 inflammation to be 21%, 50% and 27% of patients, respectively. This supports our initial hypothesis and suggests that a pharmaceutical agent targeting a single endotype will not benefit all patients with CRSsNP. A central hypothesis of this project is that inflammatory endotypes control clinical phenotypes of CRS and comorbid airway diseases, and they predict variable outcomes for pharmacological treatments. For example, we have obtained preliminary evidence showing that type 2 inflammation is selectively associated with smell loss and comorbid asthma. In addition, we found that females with CRSwNP have more severe disease than males with CRSwNP. We therefore also hypothesize that sex influences endotype, phenotype and comorbid diseases in CRS. We will collaborate with Project 1 (Immunopathology at Northwestern) and Project 3 (Epidemiology at Geisinger and Johns Hopkins) to test these hypotheses in tertiary care patients at Northwestern and to validate our hypothesis in the general population at Geisinger. Studies in Aim 1 will identify the mechanisms of inflammation for the major endotypes of CRSsNP. Studies in Aim 2 will test the hypothesis that inflammatory endotypes of CRS control clinical presentations and influence comorbidity of lower airway diseases. Studies in Aim 3 will test the hypothesis that sex influences endotype and phenotype of CRS. We believe that the proposed studies will help to identify more precise medicine strategy that effectively prevents disease in CRS patients and avoids unnecessary treatments.